Single-crystal – oriented-crystal – and epitaxy growth processes; – Processes of growth from liquid or supercritical state – Having pulling during growth
Patent
1997-02-25
2000-07-04
Kunemund, Robert
Single-crystal, oriented-crystal, and epitaxy growth processes;
Processes of growth from liquid or supercritical state
Having pulling during growth
117 81, 117944, C30B 2916
Patent
active
06083319&
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to crystals for non-linear optics, to the fabrication of these crystals and to the applications of these crystals.
2. Discussion of the Background
The crystals used in non-linear optics belong to various families, each exhibiting quite specific properties. Historically, one of the first products which appeared in this field was potassium dihydrogen phosphate (KDP). This material is still very widely used because of the relative ease of fabrication, and consequently its relatively low cost. On the other hand, KDP is very sensitive to water, which means that there are several constraints on the way in which it is used. Its second harmonic coefficient is small, which results in relatively low emission of frequency-doubled radiation. Although KDP may easily form good-sized single crystals, which may be required when it is necessary to be able to handle relatively high powers, most crystals for non-linear optics are of small size in practice. This is because they are usually produced by flux-determined growth. This is the case for BBO, LBO and KTP. In this mode, growth is very slow, requiring several weeks or even several months to reach sizes suitable for most uses.
It has been proposed to form crystals by congruent melting, using the Czochralski or Bridgman-Stockbarger techniques. This is the case, for example, for LiNbO.sub.3 crystals. LiNbO.sub.3 crystals exhibit the property of being photorefractive which, for secondharmonic generation, is a drawback. Finally, LiNbO.sub.3 crystals are very brittle. LaBGeO.sub.5 may also be formed by melting. However, it is difficult to obtain because of the appearance of undesirable phases, unless the crystallization operation is perfectly controlled. Moreover, this crystal provides only a relatively low non-linear susceptibility coefficient.
SUMMARY OF THE INVENTION
The invention therefore proposes the production of crystals for non-linear optics from their molten constituents, their melting being congruent. The invention also proposes the use of these non-linear crystals, in particular as frequency doublers or mixers or as optical parametric oscillators. The invention further proposes the use of these crystals incorporating an effective quantity of an ion for generating a laser effect for the purpose of producing self-frequency-doubling laser crystals.
According to the invention, the materials employed satisfy the general formula:
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
In the case of Ca partially substituted with Sr or Ba, this substitution is limited to the content for which parasitic phases may develop in the molten bath during crystallization, in other words limited to values for which the M.sub.4 LnO(BO.sub.3).sub.3 phase no longer exhibits congruent melting.
For compounds of the type:
For compounds of the type:
The choice of lanthanide may advantageously be determined depending on the projected use. This is because the non-linear coefficients and the birefringence of the material depend on the rare earth inserted into the matrix.
The crystals according to the invention may, as indicated previously, be doped by means of optically active lanthanide ions, such as Nd.sup.3+. The crystals in question are of formula:
z depends on the desired effect, knowing that the presence of substituent elements may lead to competition between the effects induced. The consequence of increasing the concentration is firstly to increase the laser effect. Above a certain concentration of substitution ions, progressive extinction of the emission is observed. The substituted ions become too "close" to one another and interact. In practice, substitution does not exceed 20%, and preferably not 10%. In other words, z is preferably less than 0.2 and advantageously less than 0.1. In general, the concentration is such that the lifetime is not shorter than half the maximum lifetime observable at low concentration, i.e. 99 microseconds.
The non-linear crystals used according to the invention are advantageou
REFERENCES:
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Aka et al., "A new nonlinear and neodymium laser self-frequnecy doubling crystal with congruent melting Ca4gdO(BO)3", European Journal of Solid State Inorganic chemistry, vol. 33 (80, p. 727-736, 1996.
A. B. Ilyukhin, et al., Russian Journal of Inorganic Chemistry, vol. 38, No. 6, pp. 847 to 850, "Crystal Structures of Binary Oxoborates LnCa.sub.4 O(BO.sub.3).sub.3 (Ln = Gd, Tb, Lu) and Eu.sub.2 CaO(BO.sub.3).sub.2 ", 1993.
G. J. Dirksen, et al., Journal of Alloys and Compounds, vol. 191, pp. 121 to 126, "Tetracalcium Gadolinium Oxoborate (Ca.sub.4 GdO(BO.sub.3).sub.3) As A New Host Lattice For Luminescent Materials", 1993.
R. Norrestam, et al., Chemical Mater, pp. 737-743, "Structural Investigations of New Calcium-Rare Earth (R) Oxyborates With the Composition Ca.sub.4 RO(BO.sub.3).sub.3 ", 1992.
T. N. Khamaganova, et al., Russian Journal of Inorganic Chemistry, vol. 36, No. 4, pp. 484 to 485, The Crystal Structure of Calcium Samarium Oxide Borate Ca.sub.8 Sm.sub.2 O.sub.2 (BO.sub.3).sub.6, 1991.
Aka Gerard
Bloch Laurence
Godard Jean
Kahn-Harari Andree
Salin Francois
Crismatec
Kunemund Robert
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